Historically, coffee has been brewed by passing very hot water in contact with finely ground coffee beans. Variations on this approach include use of brief hot water contact to elute only the more soluble portion of the coffee, so-called espresso, long contact between coffee and water to remove all soluble portions from the bean, so-called turkish coffee, and all manner of variants in-between. Freeze-dried coffee has also been used. The problem has been to retain fresh-brewed taste while making high volumes of the beverage; freeze-dry coffee concentrates do not retain sufficient of the delicate components of the coffee to taste like freshly brewed coffee when prepared in bulk. The alternative, normal percolation is often too slow.
The development of liquid coffee concentrates makes possible more rapid brewing of coffee by simple mixing of the concentrate and the heated water, a coffee-making process which takes no longer than than the step of mixing. Attention now turns to the heated water supply as the limiting factor in production. It is known to preheat water and release it into a liquid concentrate, but coffee quantities beyond the capacity of the water heating tank have been difficult to get rapidly owing to the long cycle involved in heating a second tank of water. Assuming a reasonable size hot water tank, the apparatus does not have enough capacity for the institutional needs mentioned above.